There are some incredible structures created by humans so long ago that it's tempting to believe they were built by alien hands. Here are some of the most famous examples of constructions that were — according to legend — created by otherworldly forces.

The Badlands Guardian (also known as Indian Head)

We weren't aware that Indians had iPods back in ancient times, but then we weren't aware…
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We weren't aware that Indians had iPods back in ancient times, but then we weren't aware that prehistoric Egyptians flew helicopters, either. It's a constant learning process. But check out this location in Google Maps or enter 50 0'38.20"N 110 6'48.32"W in Google Earth and you'll see a distinct Indian head, complete with white iPod earphones inserted. Wonder what song he's listening to?

This geomorphological feature in Alberta, Canada was discovered by Lynn Hickox on Google Earth in November 2006. The "earphones" are a road and an oil well, which were installed recently.

Nazca Lines, in the Nazca Desert, southern Peru, created between 400 and 650 AD.

There are hundreds of individual figures (sharks, lizards, orcas, hummingbirds, spiders, monkeys and more) and lines created by the Nazca culture in the 5th and 6th century, but some people says that some of these are alien landing sites and structures.

Erich von Däniken's theory is the most famous approach to solve the mystery of Nazca:

He had the idea that long time ago visitors from other stars visited the earth and naturally Nazca. At this place they landed, during the landing stones was blown away by the power of rocket propulsion. By approaching more the power was increasing and the cleaned band broader. In this way the first trapezes emerged. Later the Aliens disappeared and left confused people. Like in the modern cargo cults they tried to call the Gods back by drawing lines, figures and trapezes. Never Däniken said the formations was made by Aliens. – according to Biblioteca Pleyades.

Pyramids of Giza, near Cairo, Egypt

"During the evening of the summer solstice, from the view of the Sphinx, the sun sets right between the Great Pyramid and its neighbor. For the Egyptians to be able to do this they must have known the day of the summer solstice, and they therefore, must have known the exact length of the year, or 365.25. Again, a fact not discovered until long after the Egyptians were gone.

It is also quite strange the the Pyramids of Giza are still in almost perfect condition, while the other pyramids, which were supposedly built about 500 years later, all have sub-par masonry, and are crumbling down. An example of this is the famous ‘bent’ pyramid, which started out with the sides being built at one angle, then suddenly shifts in the middle to a shallower angle. This is because the angle at which it was started was much too steep for it to stand when finished.

A more obvious and unexplainable feat of these pyramids is the fact that each stone was around two tons, so how were the Egyptians able to build these pyramids? The wheel was not invented until later on."

"Its central claim is that there is a correlation between the location of the three largest pyramids of the Giza pyramid complex and the three middle stars of the constellation Orion, and that this correlation was intended as such by the builders of the pyramids. The stars of Orion were associated with Osiris, the sun-god of rebirth and afterlife, by the ancient Egyptians. Depending on the version of the theory, additional pyramids can be included to complete the picture of the Orion constellation, and the Nile river can be included to match with the Milky Way galaxy. The theory was first published in 1989 in Discussions in Egyptology, volume 13. It was the subject of a bestseller, The Orion Mystery, in 1994, as well as a BBC documentary, The Great Pyramid: Gateway to the Stars (February 1994), and appears in some new-age books."

Oh, and there are so many pictures about aliens ("sky god") and extraterrestrial symbols inside the pyramids:

The 6-story Derinkuyu Underground City, Turkey

This giant underground city, the biggest in Turkey is large enough to house 20,000 people with everything they want, including food stores, wine and oil presses, stables, refectories, chapels, a school, communal rooms, freeh flowing water and lots of and storage rooms.

Humans like to build cities that reach for the sky, but sometimes they also build downward. Whether …
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Maybe it was built by the Phrygians in the 8th century B.C and enlarged in the Byzantine era, but some ancient alien theorists think that it's even older and built by some ancient astronauts to protect the inhabitants of the upper city from a global disaster.

There are 1-1.5 m (3-5 ft) high and 1100 pound (500 kg) weigh circular rocks that could shut down the tunnels.

It was only discovered in the 1960s, but the site hasn't been fully excavated since then. The deepest known point of the city is around 278 ft (85 m) now.

The Great City of Teotihuacán (it means The Place Where Men Become Gods), one of the first cities of the Western Hemisphere, and the largest one before the early 15th century, now in Mexico, near Mexico City

The city which could house about 100,000 people was built by hand more than a thousand years before the Aztecs arrived. it reached its zenith between 100 BC and the mid-7th century. It was built by the Toltecs, or some cultures together, including the Maya, Zapotec and Mixtec. They had complex mathematical and astronomical knowledge and there are some similarities to the Great Pyramids of Egypt.

But some ancient alien theorists have pointed out (okay, I mean Erich von Däniken) that the city was probably built by space aliens, the originals of the gods, and they lived here "even before homo sapiens existed".

These are the strangest things here:

The city is meticulously laid out on a grid which is offset 15º.5 from the cardinal points. Its main avenue, the "Street of the Dead," runs from 15º.5 east of north to 15º.5 west of south, while its most impressive structure, the Pyramid of the Sun, is directly oriented to a point 15º.5 north of west — the position at which the sun sets on August 13.

- The Pyramid of the Sun is exactly half as tall as the Pyramid of Giza and the Temple of the Sun, the Temple of the Moon, and the Temple of Quetzalcoatl are in the same layout as Orion’s Belt.

- One of the most interesting things about Teotihuacan is the finding by archaeologists of the extensive use of mica embedded in numerous structures. This mineral is found 3,000 miles away in Brazil and it is found in all buildings, housing complexes, temples and along the roads so basically this mineral is all over Teotihuacan. The pyramid of the Sun in Teotihuacan contained considerable amounts of mica in layers up to 30 cm (11.8 in). This silicate mineral is stable when exposed to electricity, light, moisture, and extreme temperatures.

The extremely fragile mica was only used inside the pyramids, but why? Because the aliens had electricity, of course!

The Trilithon of Baalbek, Lebanon

The three horizontally lying giant stones, the part of the podium of the Jupiter temple are weighing 800 tons each and some others around them weighing around 350 tons. In the quarry nearby is an unused 1,000 t block.

Ancient alien theorists, such as Georgio Tsoukalos and David Childress (as seen on the History channel’s Ancient Aliens, The Series) suggest that various advanced technologies were used to move these stones, such as anti-gravity technology, and even acoustic levitation.

Stonehenge, Wiltshire, England

This ring of standing stones was built between 3000 BC and 2000 BC. The weight of the standing stones are up to 50 tons.

Its exact function isn't clear, but maybe it was a place of healing, a cemetery for the elite, a soundscape, a celestial observatory or just a simple monument that was intended to unify the different people of the British Island. Nobody knows that, but Däniken is sure that it's an alien landing pad, because only they could move those stones for 100 miles.